1. Field of the Invention
This invention concerns a supercharger thrust bearing such as is used in boats and ships.
2. Description of the Related Art
FIGS. 3A and 3B in the attached Drawings illustrate a conventional supercharger thrust bearing 51. FIG. 3A is a sectional view and FIG. 3B is a front view. As diagramed, the conventional thrust bearing 51 used in a supercharger is in contact with a thrust collar 53 attached to a turbine shaft 52, so that it receives the thrust forces to which the turbine shaft is subjected. The thrust collar 53 turns together with the turbine shaft 52, and lubricating oil is supplied to a pad surface 54 of the thrust bearing 51 to reduce the thrust resistance and prevent the temperature of the pad surface 54 from rising.
A thrust bearing support 55 holds the thrust bearing 51 stationary. A plurality of oil supply passageways 56 are formed in the thrust bearing support 55 for the purpose of supplying the lubricating oil. The oil passageways 56 extend generally radiantly, spaced from each other in a circumferential direction. Another plurality of oil supply passageways 57 are formed in the thrust bearing 51 such that they communicate with the oil supply passageways 56 at upstream ends thereof (left ends in the drawing) and open to the pad surface 54 at downstream ends thereof (right ends in the drawing) respectively. Oil supply grooves 59 are formed to extend radiantly from open ends 58 of the oil supply passageways 57. These oil supply grooves 59 have a certain groove depth, and extend as far as the vicinity of the periphery of the thrust bearing 51. At the outer radial ends in the thrust bearing 51, another grooves 61 are formed having a shallower depth than the oil supply grooves 59.
The lubricating oil that is supplied from the oil supply passageways 56 and 57 flows outward in the radial direction inside the oil supply grooves 59, and, by the turning of the thrust collar 53, flows to the pad surface 54. Then, the lubricating oil that flows over the pad surface 54 flows out to the outside through gaps 62 formed between the shallow grooves 61 and the thrust collar 53. In this manner, the cool lubricating oil (new oil) is expected to be supplied over the entire pad surface 54. The lubrication oil is caused to move in the circumferential direction on the pad surface 54 upon rotations of the thrust collar 53 (or the turbine shaft 52) as indicated by the arrows X).
When the thrust bearing 51 described above has been used in automobile turbochargers, it has been possible to supply lubricating oil effectively to the pad surface 54.
In superchargers used in boats, ships and the like, however, which are operated under a high pressure ratio, the turning speed of a rotating shaft is high, so that the circumferential speed at the periphery of the thrust bearing is very high. As a result, a problem arises in that the new oil is not supplied adequately to the pad surface 54.
More specifically, at a high circumferential speed, the lubricating oil heated on one pad surface 54 rides over the cool lubricating oil (new oil) inside the adjacent oil supply groove 59 and penetrates to the next pad surface 54. Consequently, the temperature of the pad surface 54 readily rises.